Switched capacitor converters are often used as voltage regulators to provide stable voltage sources for low voltage applications. When used in electronic applications having physical size constraints, such switched capacitor converters are often implemented using integrated circuits together with external capacitors.
However, such switched capacitor converters are limited to providing low load currents for the low voltage applications. With emerging low voltage applications requiring higher load currents to drive more demanding applications, conventional switched capacitor converters are simply unable to deliver the higher load currents required.
One example of a conventional low voltage application requiring higher load currents is miniature hard disk drives, such as the IBM Microdrive. Such miniature hard disk drives are typically low voltage devices having a processor powered by a switch capacitor converter. The switched capacitor converter in miniature hard disk drives is also necessarily smaller than typical converters.
An example of one implementation of a conventional switched capacitor converter is shown in FIG. 1. The circuit includes pumping capacitor 15, load capacitor 17, two pairs of semiconductor switches (11, 14 & 12, 13) and DC voltage source 22. Switched capacitor converter 10 operates on the principle of charge balance transfer. The two pairs of semiconductor switches (11, 14 & 12, 13) are configured to operate switched capacitor converter 10 by continuously alternating between a charging stage and a discharging stage.
In the charging stage, the first pair of semiconductor switches (11, 14) are closed, and the second pair of semiconductor switches (12, 13) are opened, coupling DC voltage source 22 to pumping capacitor 15. Pumping capacitor 15 is further coupled in series to load capacitor 17. Thus, in the charging state both capacitors, pumping capacitor 15 and load capacitor 17, are charged.
In the discharging stage, the first pair of semiconductor switches (11, 14) are opened, and the second pair of semiconductor switches (12, 13) are closed, de-coupling pumping capacitor 15 from DC voltage source 22. Pumping capacitor 15 remains coupled to load capacitor 17. In this stage, pumping capacitor 15 discharges to load capacitor 17, while load capacitor 17 continues to provide current to the attached application. The continuous alternating charging and discharging stages of conventional switched capacitor converter 10 regulates the desired voltage of the attached application.
Conventional switched capacitor converters allow for only low load currents to be drawn by the application. Increasing the ratings of pumping capacitor 15 and load capacitor 17 allow higher load currents and results in the increase of the physical size of pumping capacitor 15 and load capacitor 17 and the overall architecture.
Other implementations of conventional switched capacitor converter include adding additional pumping capacitors by cascading them and having additional semiconductor switches to couple them together during the charging and discharging phases. However, such implementations require the use of more semiconductor switches and also an increase in the physical size of the overall architecture.
Therefore, there is a need for an improved switched capacitor converter architecture having size constraints for driving high load currents for low voltage applications.